The present invention relates to a printer for forming an image on a continuous paper.
Conventionally, know are copy machines, laser beam printers and the like which perform printing is by an electrophotographic method, wherein a uniformly charged photoconductive material on the surface of a photoconductive drum is exposed to form a latent image by partially removing charges therefrom. Charged toner is then adhered to the latent image and developed (forming a toner image), and the developed toner image is transferred to a recording paper and fixed thereon by a fixing unit.
Some printers making use of the electrophotographic method print images on a continuous folded paper referred to as fanfold paper (hereinafter, simply abbreviated as a continuous paper), which Is provided with feed holes along the side edges thereof, fed in an alternatively folded state for each page, and is further provided with a perforated tear line defined along each folded line thereof so that the paper can be easily cut off.
The printer making use of the electrophotographic method generally employs a heat roll fixing unit as a fixing unit by which toner is fixed onto a recording paper. The heat roll fixing unit includes a pair of fixing rollers pressed against each other, one of the which is a heat roller which can be heated. Thus, when a recording paper on which unfixed toner is placed is positioned between the pair of the fixing rollers and heated by the heat roller, the toner is heated and melted. When, however, this type of heat roll fixing unit is used in a printer which prints on continuous paper, a disadvantage may arise in that the recording paper, (continuous paper) waiting for a printing operation, held between the heat roller and the press roller, is burnt or makes a blister at the same position thereof due to tile heat supplied from the heat roller. In particular this disadvantage is liable to arise when the heat control system (a temperature sensor, control unit) for the heat roller is out of order. Therefore, it is contemplated that one of the pair of the fixing rollers (preferably the heat roller) be arranged to be retracted so that the roller can be retracted when the continuous paper waits for printing.
Further, when the printer employs a rotating photoconductive drum, a toner image is transferred when the exposed position of the photoconductive drum is rotated to a position confronting a recording paper (that is, the exposed position of the photoconductive drum is different from the position at which the toner image is transferred from the photoconductive drum to the continuous recording paper in the peripheral direction of the photoconductive drum), and thus the photoconductive drum must be moved with respect to the continuous paper (to select a desired portion of the continuous paper) prior to a printing operation in order to start a print at a position of the continuous paper spaced apart from the perforated tear line thereof (i.e., the front edge of a page) by a predetermined distance. When the continuous paper is in an image transfer state (the continuous paper is abutted against the surface of the photoconductive drum) while the image transfer is performed, a problem arises in that photoconductive material on the surface of the photoconductive drum is scratched or worn by the continuous paper. Further toner remaining on the surface of the photoconductive drum is adhered to the continuous paper and causes extraneous matter to appear on the paper (i.e., makes the paper appear "dirty"). To cope with this problem, it is contemplated that a transfer charger be arranged to be retracted from a transfer position so that it is retracted while the continuous paper waits for a printing.
Nevertheless, with the above arrangement in which the transfer charger and fixing roller can be retracted from the transfer position and fixing position, respectively, there is no ability to keep the continuous paper in an unmovable state. Rather the portion of the continuous paper which is intended to be stopped at a predetermined position while waiting for the resumption of a printing operation, is moved by a force applied to the continuous paper to cut off a printed and discharged page thereof along a perforated tear line. Thus when the printing operation is resumed, a printing is started from an offset position of the continuous paper.